Apparatus and method for controlling an electrical switch array

ABSTRACT

An electrical switching apparatus configured for low power operation includes: (a) a plurality of switching devices arranged in a switching array permitting sensing of individual switching events by selected switching devices; (b) a switching control device coupled with the switching array that provides power to the switching array for sensing and for a first time interval after a first switching device is actuated. The control device identifies the first switching device during the first time interval and interrupts power to the switching array after the first time interval until the first switching device is deactuated. The control device provides power to the switching array for a second time interval after the first switching device is deactuated. The control device determines during the second time interval whether a second switching device other than the first switching device is actuated.

This application claims priority under 35 USC § 119(e)(1) of provisionalapplication Ser. No. 60/329,774, filed Oct. 15, 2001.

BACKGROUND OF THE INVENTION

The present invention is directed to electrical switch arrays, andespecially to electrical keyswitch arrays, or keypads, of the sort usedfor portable devices, such as portable telephones, wireless telephones,personal digital assistant (PDA) devices and similar devices.

Often during use of such products a condition occurs where one or morekeys is stuck or otherwise held in an actuated position. For example, awireless phone in the bottom of a user's purse or in a user's pocket mayhave one or more of the keys in its keypad array inadvertently pressedand held down (i.e., in an actuated position) for a long period of time.Depending upon the circuit design and implementation of the keypadinterface such a holding down of a keyswitch can draw power and causeexcess current to flow. Excess current flow can prematurely drain thebatteries in battery-operated products such as wireless phones, PDAdevices and similar products.

Previous solutions to this problem of inadvertent current drain haveinvolved having a microprocessor or similar computing device “wake up”the system from a “sleep” mode. The sleep mode is a mode in which onlyminimal activity is carried out by an apparatus in order that onlyminimal power is required so that minimal current drain occurs. Thedevice is “awakened” periodically every 10-20 μsec (microseconds) andpolling or other examination of the keypad is carried out to determinewhether a key is being held down. If a key is determined to be helddown, the device remains awake and processes the information imparted bythe holding down of the key. The problem with such prior art solutionsis that the required periodic “awakening” and the repeated pollingconsume a certain amount of power and therefore cause current drain thatshortens battery life.

There is a need for an apparatus and method for controlling anelectrical switch array that requires less power to operate than isrequired by presently available control apparatuses and methods.

SUMMARY OF THE INVENTION

An electrical switching apparatus configured for low power operationincludes: (a) a plurality of switching devices arranged in a switchingarray permitting sensing of individual switching events by selectedswitching devices; (b) a switching control device coupled with theswitching array that provides power to the switching array for sensingand for a first time interval after a first switching device isactuated. The control device identifies the first switching deviceduring the first time interval and interrupts power to the switchingarray after the first time interval until the first switching device isdeactuated. The control device provides power to the switching array fora second time interval after the first switching device is deactuated.The control device determines during the second time interval whether asecond switching device other than the first switching device isactuated.

The preferred embodiment of the invention is configured to provide thatthe control device responds to a second switching device being actuatedduring the second time interval by identifying the second switchingdevice during the second time interval. The control device theninterrupts power to the switching array after the second time intervaluntil the second switching device is deactuated. The invention mayinclude an internal or an external time reference. The preferredembodiment of the invention employs an internal digitally controlledoscillator (DCO) for establishing timing for operation of the apparatus.

A method for operating an electrical switching apparatus that includes aplurality of switching devices arranged in a switching array configuredto permit sensing of individual switching events by selected switchingdevices of the plurality of switching devices includes the steps of: (a)detecting when a first switching device is actuated; (b) providing powerto the switching array for sensing and for a first time interval afterthe first switching device is actuated; (c) identifying the firstswitching device during the first time interval; (d) interrupting powerto the switching array after the first time interval until the firstswitching device is deactuated; (e) providing power to the switchingarray for a second time interval after the first switching device isdeactuated; and (f) determining during the second time interval whethera second switching device other than the first switching device isactuated.

Preferably, the method includes the further steps of: (g) when a secondswitching device is actuated during the second time interval,identifying the second switching device during the second time interval;(h) interrupting power to the switching array after the second timeinterval until the second switching device is deactuated; and (i) whenno second switching device is actuated during the second time interval,restoring power to the switching array after the second time interval.

It is therefore an object of the present invention to provide anapparatus and method for controlling an electrical switch array thatrequires less power to operate than is required by presently availablecontrol apparatuses and methods.

Further objects and features of the present invention will be apparentfrom the following specification and claims when considered inconnection with the accompanying drawings, in which like elements arelabeled using like reference numerals in the various figures,illustrating the preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating the preferred embodiment ofthe present invention employed with an exemplary keyswitch array.

FIG. 2 illustrates selected timing diagrams associated with operation ofthe apparatus illustrated in FIG. 1.

FIG. 3 is a flow diagram illustrating the method of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The preferred embodiment of the apparatus of the present inventionemploys a microprocessor device that responds to rising and fallingedges of signals. In the illustrative descriptions presented herein theapparatus is described as having a first response to a rising signaledge and a second response to a falling signal edge. Those skilled inthe art of microprocessor system design will readily recognize that suchan implementation is only exemplary and that a microprocessor could aseasily be employed to respond with the second response to a risingsignal edge and the first response to a falling signal edge.

FIG. 1 is a schematic diagram illustrating the preferred embodiment ofthe present invention employed with an exemplary keyswitch array. InFIG. 1, a system 10 includes a control unit 12 and an electrical switcharray 15. Electrical switch array 15 is arranged in a plurality of rowsn, such as rows 20, 22, 24, 26 and a plurality of columns m, such ascolumns 30, 32, 34. A plurality of switches 50 _(nm) is connected inswitch array 15 with each respective switch 50 _(nm) being coupled at alocus identifiable by a unique (row n, column m) combination. Thuselectrical switch array 15 includes switches 50 ₁₁ (row 1, column 1), 50₁₂ (row 1, column 2), 50 ₁₃ (row 1, column 3) in row 20. Electricalswitch array 15 further includes switches 50 ₂₁ (row 2, column 1), 50 ₂₂(row 2, column 2), 50 ₂₃ (row 2, column 3) in row 22. Electrical switcharray 15 further includes switches 50 ₃₁ (row 3, column 1), 50 ₃₂ (row3, column 2), 50 ₃₃ (row 3, column 3) in row 24. Electrical switch array15 further includes switches 50 ₄₁ (row 4, column 1), 50 ₄₂ (row 4,column 2), 50 ₄₃ (row 4, column 3) in row 26.

Row 20 is coupled with control unit 12 via a line 40, a seriallyconnected diode element 41 and a line 70. Row 22 is coupled with controlunit 12 via a line 42, a serially connected diode element 43 and a line72. Row 24 is coupled with control unit 12 via a line 44, a seriallyconnected diode element 45 and a line 74. Row 26 is coupled with controlunit 12 via a line 46, a serially connected diode element 47 and a line76.

Column 30 is coupled with control unit 12 via a line 31; line 31 is alsocoupled with ground 61 via a serially connected impedance 60. Column 32is coupled with control unit 12 via a line 33; line 33 is also coupledwith ground 63 via a serially connected impedance 62. Column 34 iscoupled with control unit 12 via a line 35; line 35 is also coupled withground 65 via a serially connected impedance 64.

Control unit 12 includes a sensing portion 14 and a switching portion16. Control unit 12 is configured (as by, for example, including amicroprocessor device, not shown in detail in FIG. 1) to maintain system10 in a low power mode, commonly referred to as a “sleep” mode in whichonly minimal power is consumed, until a signal edge from one of theswitches 50 _(nm) is sensed by sensing portion 14 via a line 31, 33, 35.When a signal edge, for example a rising edge, is sensed by sensingportion 14, control unit 12 “wakes up” because system 10 is configuredso that a rising signal edge indicates that a first-actuated switch 50_(nm1) is pressed, or actuated. That is, switching portion 16 of controlunit 12 switchingly connects switch array 15 to power in order thatcontrol unit 12 may isolate the particular (row n, column m) locus atwhich first-actuated switch 50 _(nm1) is situated. Preferably controlunit 12 will delay a predetermined time interval in order to assure thatdebouncing or other settling of signals from first-actuated switch 50_(nm1) is complete so that spurious signals may be avoided. A typicalrepresentative debounce interval is approximately 40-80 msec.

Control unit 12, by cooperation of sensing unit 14 and switching unit16, isolates the (row n, column m) locus of first-actuated switch 50_(nm1) that generated the rising edge signal that “awoke” control unit12. This isolation of (row n, column m) locus uniquely identifiesfirst-actuated switch 50 _(nm1), and that identity can be used forfurther processing in the host apparatus (not shown in FIG. 1) in whichsystem 10 is employed, such as a wireless phone, a personal digitalassistant (PDA) device or another host apparatus. When identification offirst-actuated switch 50 _(nm1) is complete, control unit 12 returns toa “sleep” mode until first-actuated switch 50 _(nm1) is released, ordeactuated. Releasing first-actuated switch 50 _(nm1) generates anotheredge signal; in this exemplary illustration a falling edge signal isgenerated. When sensing portion 14 of control unit 12 detects thatfirst-actuated switch 50 _(nm1) is released, control unit 12 preferably“reawakens”, imposes another debounce interval and then checks to seewhether another second-actuated switch 50 _(nm2) has been depressedwhile control unit 12 was awaiting deactuation of first-actuated switch50 _(nm1). If a second-actuated switch 50 _(nm2) has been actuated,control unit 12 will identify second-actuated switch 50 _(nm2) andproceed as before described in connection with first-actuated switch 50_(nm1). That is, control unit 12 identifies second-actuated switch 50_(nm2) and returns to “sleep” mode until another falling edge signalindicates that second-actuated switch 50 _(nm2) is deactivated orreleased.

If no second switch has been actuated while control unit 12 was awaitingdeactuation of first-actuated switch 50 _(nm1), then control unit 12returns to a “sleep” mode to await a rising edge signal indicatingactuation of a second-actuated switch 50 _(nm2).

The above described cycle of scanning switch array 15, detection ofactuation of a switch 50 _(nm) and identification of the (row n, columnm) locus of the actuated switch 50 _(nm) takes approximately 50 μsec.Thus, scanning, identification and debounce interval occupyapproximately 40-80 msec. A typical typist or keyboard operator actuateskeyswitches at a speed resulting in a depressed, or actuated timeinterval for a keyswitch of approximately 100-200 msec (milliseconds); aspeed typist using a standard keyboard may be able to actuate keys at aspeed resulting in a depressed time interval of 40-50 msec. The devicesfor which the preferred embodiment of the invention is used—portabledevices such as wireless phones, PDA devices or similar devices—presentsmall keyswitch arrays that are not conducive to actuation speeds asfast as may be encountered in the case of a typist using a standardkeyboard. Thus, the duration of a depressed or actuated key is likely tobe significantly longer than the 40-80 msec required for scanning,identification and debounce intervals expected when using the presentinvention.

In the preferred embodiment of the invention the required timing iseffected using a digitally controlled oscillator (DCO). That is, timingis generated and controlled by a cooperative employment of software andsupporting hardware, not a crystal. Using such a DCO-based timing sourceand control and not requiring even the small amount of power that isrequired for powering a crystal ensures that very little power isconsumed while control unit 12 is in a “sleep” mode. Even during most ofthe interval when a switch is actuated, control unit 12 is in “sleep”mode in which only minimal power is consumed. The apparatus and methodof the present invention is very power efficient.

FIG. 2 illustrates selected timing diagrams associated with operation ofthe apparatus illustrated in FIG. 1. In FIG. 2, a graphic plot 110 isillustrated including a first signal curve 120 representing a signal,such as voltage or current, sensed across keyswitch array 15 and asecond signal curve 150 representing a signal, such as voltage orcurrent, indicating the state of control unit 12 (FIG. 1). Signal curves120, 150 are plotted against a common time axis 112 and an amplitudeaxis 114. Amplitude axis 114 may have separate parameter ranges forsignal curves 120, 150 (not shown in FIG. 2). An important point to beillustrated by FIG. 2 is the mutual relationships of timing of signalcurves 120, 150 during operation of apparatus 10 (FIG. 1).

During a time interval t₀-t₁, no keyswitch 50 _(nm) is actuated inswitch array 15; signal curve is at a first value 122 and signal curve150 is at a first value 152. At a time t₁, a first keyswitch 50 _(nm1)in switch array 15 actuated and signal curve 120 increases to a secondvalue 124 greater than first value 122. The increase in value of signalcurve 120 from first value 122 to second higher value 124 establishes aleading edge for signal curve 120 at time t₁. Control unit 12 isconfigured to recognize a leading edge pattern in signal curve 120 andreacts by “awakening” from “sleep” mode. Accordingly, signal curve 150rises from a first value 152 to a second higher value 154 at time t₁. Asdescribed earlier in connection with FIG. 1, control unit 12 waits ashort time interval t₁-t₂ to permit first keyswitch 50 _(nm1) todebounce. During a remaining active interval t₂-t₃ for control unit 12,control unit 12 identifies which keyswitch is actuated first keyswitch50 _(nm1). The information identifying which keyswitch is actuated firstkeyswitch 50 _(nm1) is passed on to a host apparatus (not shown inFIG. 1) for further use in operating the host apparatus such as dialinga phone number, entering data or for another function performed by thehost apparatus.

At a time t₃, control unit 12 returns to “sleep” mode during which onlyminimal power is required for operating control unit 12; signal curve150 returns to lower level 152. As mentioned earlier, control unit 12preferably establishes timing using a digitally controlled oscillator(DCO) so that very little power is required by control unit 12 in its“sleep” mode and, indeed, in other operating modes as well.

Signal curve 150 remains at lower level 152 (i.e., control unit 12remains in “sleep” mode) until first keyswitch 50 _(nm1) is released, ata time t₄. Release of first keyswitch 50 _(nm1) causes signal curve 120to return to lower level 122 from higher level 124, thereby establishinga lagging edge for signal curve 120 at time t₄.

Control unit 12 remains in its “sleep” mode, as indicated by signalcurve 150 remaining at lower level 152, until a lagging edge is detectedin signal curve 120 at time t₄. Thus, at time t₄, signal curve 150 risesto higher level 154, indicating that control unit 12 has noted thatfirst keyswitch 50 _(nm1) is deactuated and control unit 12 has“awakened” from its “sleep” mode. Control unit 12 waits a short timeinterval t₄-t₅ to permit any second keyswitch 50 _(nm2) that may havebeen actuated during the interval t₃-t₄ to debounce. During a remainingactive interval t₅-t₆ for control unit 12, control unit 12 determineswhether a second keyswitch 50 _(nm2) is actuated and if so, identifyingwhich keyswitch is the actuated second keyswitch 50 _(nm2). Theinformation identifying which keyswitch is the actuated second keyswitch50 _(nm2) is passed on to a host apparatus (not shown in FIG. 1) forfurther use in operating the host apparatus such as dialing a phonenumber, entering data or for another function performed by the hostapparatus.

If a second keyswitch 50 _(nm2) has been actuated, control unit 12proceeds anew as described earlier to await deactuation of secondcontrol switch 50 _(nm2) as indicated by a lagging edge in signal curve120 and subsequent checking (after a debounce period) whether a thirdkeyswitch 50 _(nm3) has been actuated. If no second keyswitch 50 _(nm2)is detected by control unit 12 during interval t₅-t₆ as having beenactuated, control unit 12 returns to a state essentially as existsduring time interval t₀-t₁ to await actuation of a second keyswitch 50_(nm2).

The description of operation of system 10 (FIG. 1) in connection withsignal curves 120, 150 (FIG. 2) is a representative implementation. Oneskilled in the art of digital control system design can use theteachings of this disclosure to design a system in which one or both ofsignal curves 120, 150 deviate from a higher signal level to a lowersignal level, or even to different signal levels, in response toconditions in switch array 15. Such changes in signal definitions andconsequent logical events by control unit 12 in response to signalvariations are regarded as within the scope of the apparatus and methodof the present invention so long as control system 12 “awakens” onnoticing actuation of a switch in switch array 15, identifies theparticular switch activated and returns to “sleep” mode to “reawaken”when deactuation of the switch is noted.

FIG. 3 is a flow diagram illustrating the method of the presentinvention. In FIG. 3, a method 300 for operating an electrical switchingapparatus that includes a plurality of switching devices arranged in aswitching array configured to permit sensing of individual switchingevents by selected switching devices begins at a RESET locus 302. Method300 continues with an initializing step to ensure that signal levels inthe electrical switching apparatus are at proper initial levels, asindicated by a block 304. Method 300 continues by awaiting an indicationof key activity in the switching array, as indicated by a block 306. Asdescribed earlier in connection with FIGS. 1 and 2, a representativeindication of key activity is a leading edge in a particular signalassociated with the switch array. Method 300 inquires whether such anindication of key, or switch, activity has occurred, as indicated by aquery block 308 posing the query, “Has there been an indication of keyactivity?”

If there has been no indication of key activity, method 300 proceedsaccording to NO response line 310 to return to block 306 and method 300continues to await an indication of key activity. If there has been anindication of key activity, method 300 proceeds according to YESresponse line 312. A debounce delay interval is imposed by method 300,as indicated by a block 314, to ensure accurate indication by detectedsignal levels and to guard against erroneous indications that may beoccasioned by noise or other spurious signal components.

Method 300 continues by providing power to the switching array for afirst time interval after the first switching device is actuated andscanning the switching array, as indicated by a block 316. Method 300then poses a query, as indicated by a query block 318, whether a key, orswitch was actually pressed, or actuated. If no key has been actuated,method 300 proceeds via NO response line 320 to return to awaiting keyactivity, as indicated by block 306. If a key has been actuated, method300 proceeds via YES response line 322 and a determination, oridentification is made as to which particular switch was depressed, asindicated by a block 324. Method 300 continues by returning to sleepmode, interrupting power to the switching array and awaiting release ofthe actuated key, as indicated by a block 326. Method 300 poses a query,as indicated by a query block 328, whether there has been a key releaseindication, (e.g., a lagging edge in signal curve 120; FIG. 2). If therehas been no key release indication, method 300 proceeds via NO responseline 330 to continue awaiting release of a key, as indicated by block326. If there is a key release indication, method 300 proceeds via YESresponse line 332. A debounce delay interval is imposed by method 300,as indicated by a block 334, to ensure accurate indication by detectedsignal levels and to guard against erroneous indications that may beoccasioned by noise or other spurious signal components.

Method 300 continues by providing power to the switching array for asecond time interval after the first switching device is actuated andscanning the switching array, as indicated by a block 336. Method 300then poses a query, as indicated by a query block 338, whether a secondkey, or switch was actually pressed, or actuated during the time method300 was awaiting key release (block 326). If a second key has beenactuated, method 300 proceeds via YES response line 340 to return toidentify which key is the second key depressed, as indicated by block324. Method 300 continues from that juncture as previously describedregarding blocks 328, 334, 336, 338 in connection with the second keyactuated. If no second key has been actuated, method 300 proceeds via NOresponse line 342 to await actuation of a second key according to block306. Method 300 then proceeds from block 306 in the manner previouslydescribed as it relates to actuation of a second key.

It is to be understood that, while the detailed drawings and specificexamples given describe preferred embodiments of the invention, they arefor the purpose of illustration only, that the apparatus and method ofthe invention are not limited to the precise details and conditionsdisclosed and that various changes may be made therein without departingfrom the spirit of the invention which is defined by the followingclaims.

1. An electrical switching apparatus configured for low power operation;the apparatus comprising: (a) a plurality of switching devices; saidplurality of switching devices being arranged in a switching arraypermitting sensing of individual switching events by selected switchingdevices of said plurality of switching devices; (b) a switching controldevice coupled with said switching array; said control device providingpower to said switching array for said sensing and for a first timeinterval after a first said switching device of said plurality ofswitching devices is actuated; said control device identifying saidfirst switching device during said first time interval; said controldevice interrupting power to said switching array after said first timeinterval until said first switching device is deactuated; said controldevice providing power to said switching array for a second timeinterval after said first switching device is deactuated; said controldevice determining during said second time interval whether a secondsaid switching device of said plurality of switching devices other thansaid first switching device is actuated.
 2. An electrical switchingapparatus configured for low power operation as recited in claim 1wherein said control device responds to a second said switching deviceof said plurality of switching devices being actuated during said secondtime interval by identifying said second switching device during saidsecond time interval; said control device interrupting power to saidswitching array after said second time interval until said secondswitching device is deactuated.
 3. An electrical switching apparatusconfigured for low power operation as recited in claim 2 wherein saidcontrol device responds to no second said switching device of saidplurality of switching devices being actuated during said second timeinterval by restoring power to said switching array after said secondtime interval.
 4. An electrical switching apparatus configured for lowpower operation as recited in claim 1 wherein said control deviceresponds to no second said switching device of said plurality ofswitching devices being actuated during said second time interval byrestoring power to said switching array after said second time interval.5. A switching control apparatus for controlling an electrical keyswitcharray including a plurality of keyswitches; the apparatus comprising:(a) a switching control device coupled with said keyswitch array; saidswitching control device controlling application of electrical power tosaid keyswitch array; and (b) a sensing device coupled with saidkeyswitch array; said sensing device cooperating with said switchingdevice to effect periodic sensing of respective keyswitches of saidplurality of keyswitches; said switching control device providing saidelectrical power to said keyswitch array for said sensing and during afirst time interval after a first keyswitch of said plurality ofkeyswitches is actuated; said sensing device identifying said firstkeyswitch during said first time interval; said switching deviceinterrupting power to said keyswitch array after said first timeinterval until said sensing device senses said first keyswitch isdeactuated; said switching device providing said electrical power tosaid keyswitch array for a second time interval after said firstkeyswitch is deactuated; said sensing device sensing during said secondtime interval whether a second said keyswitch of said plurality ofkeyswitches other than said first keyswitch is actuated.
 6. A switchingcontrol apparatus for controlling an electrical keyswitch arrayincluding a plurality of keyswitches as recited in claim 5 wherein saidsensing device responds to a second said keyswitch of said plurality ofkeyswitches being actuated during said second time interval byidentifying said second keyswitch during said second time interval; saidswitching device responding to said second keyswitch being actuatedduring said second time interval by interrupting power to said keyswitcharray after said second time interval until said second keyswitch isdeactuated.
 7. A switching control apparatus for controlling anelectrical keyswitch array including a plurality of keyswitches asrecited in claim 6 wherein said switching device responds to no secondkeyswitch of said plurality of keyswitches being actuated during saidsecond time interval by restoring power to said keyswitch array aftersaid second time interval.
 8. A switching control apparatus forcontrolling an electrical keyswitch array including a plurality ofkeyswitches as recited in claim 5 wherein said switching device respondsto no second keyswitch of said plurality of keyswitches being actuatedduring said second time interval by restoring power to said keyswitcharray after said second time interval.
 9. A method for operating anelectrical switching apparatus; said electrical switching apparatusincluding a plurality of switching devices arranged in a switchingarray; said switching array being configured to permit sensing ofindividual switching events by selected switching devices of saidplurality of switching devices; the method comprising the steps of: (a)detecting when a first switching device of said plurality of switchingdevices is actuated; (b) providing power to said switching array forsaid sensing and for a first time interval after said first switchingdevice is actuated; (c) identifying said first switching device duringsaid first time interval; (d) interrupting power to said switching arrayafter said first time interval until said first switching device isdeactuated; (e) providing power to said switching array for a secondtime interval after said first switching device is deactuated; and (f)determining during said second time interval whether a second saidswitching device of said plurality of switching devices other than saidfirst switching device is actuated.
 10. A method for operating anelectrical switching apparatus as recited in claim 9 wherein the methodcomprises the further steps of: (g) when a second said switching deviceis actuated during said second time interval, identifying said secondswitching device during said second time interval; and (h) interruptingpower to said switching array after said second time interval until saidsecond switching device is deactuated.
 11. A method for operating anelectrical switching apparatus as recited in claim 9 wherein the methodcomprises the further steps of: (g) when no second said switching deviceis actuated during said second time interval, restoring power to saidswitching array after said second time interval.